ABSTRACT
Atrypide brachiopods originated during the late Llanvirn (Llandeilo) benthic ‘shelly’ radiation: the last taxa disappeared towards the Frasnian-Famennian extinction boundary, so that the order endured for close to 90 Ma, commonly numerically dominating many other brachiopods and forming distinctive, shallow-water communities. All ca. 200 genera or subgenera described are known to have been confined to tropical climates, with many preferentially occurring in subtidal carbonate shelf and ramp inhabitants. Using generic diversity compilation at the stage level, including synonymies, the Caradoc and Ashgill mark a slow rise and arrival of the major suborders and families. The Anazygidina, primitive Protozygidae and Cyclospiridae, which dominated to near the Ordovician-Silurian boundary mass extinction events, were taken over by the ribbed ‘Atrypa group’ (suborder Atrypidina) and advanced smooth shelled forms (Lissatrypidina) in the latest Ordovician and Early Silurian. By the late Llandovery (Telychian), 27 genera had proliferated, including many smoothshelled taxa, the largest expansion of the Atrypida during their history, with a diversity maintained to the end of the Ludlow-Pridoli. The Early Devonian (Lochkov) saw a decline to 19 genera, with a slow return by the end of the Pragian, a tectonically active phase marked by global sea-level drawdowns, and provinciality. The late Emsian-Eifelian marked a peak in atrypoid diversity, reaching a maximum of 47 genera, coinciding with a global greenhouse setting and reef expansion, with many taxa specifically adapted to and confined to reefal carbonates (notable the Davidsoniidina). Diversity declined in the mid-Givetian, and was reduced by 50% towards the end-Givetian, with dramatic losses of reefal taxa, many at the family level, and the apparently complete loss of the Davidsoniidina. The Frasnian was a stage of low diversity (14 genera), though there was local high abundance especially in mid-Frasnian time, up to the late Frasnian Palmatolepis rhenana conodont zone. Long-lived, cosmopolitan taxa dominated in the Frasnian, with some new arrivals within the family Atrypidae. Within the latest Frasnian P. linguiformis Zone, most regions saw fewer than two or three genera prevailing: there are no mass ‘death horizons’ known, and declines were stepdown events, probably tied into climatic cooling, sea-level drawdowns and intermittent highstands, with virtual absence of atrypids in the uppermost metres of strata in unbroken F/F successions. There are no Atrypida known from the Famennian, except as reworked Frasnian shells.
